erroneous comment describing range-separated exx parameter beta

[evaleev]

in https://github.com/wavefunction91/ExchCXX/blame/master/include/exchcxx/xc_functional.hpp#L69 : should this be alpha + beta? E.g. LCWPBE alpha=1 beta=-1, so only the long-range (erf) part is kept.

[wavefunction91]

That is correct.